1. Field of the Invention
The present invention relates to harvesting machines (such as combine harvesters) and has particular reference to tailings rethresher means in such machines.
While the terms "grain" and "straw" are used principally throughout this specification for convenience it should be understood that the terms are not intended to be limiting. Thus, "grain" refers to that part of the crop material which is threshed and separated from the discardable part of the crop material which is referred to as "straw".
2. Description of the Prior Art
In known combine harvesters, grain is threshed and separated in a threshing and separating mechanism and the separated grain, together with impurities of all kinds, such as chaff, dust, straw particles, tailings (incompletely threshed ears), is fed to a cleaning mechanism for cleaning. Clean grain is collected there-below and fed to a grain tank for temporary storage. The tailings are separated from the clean grain and impurities for reprocessing. In some known combines, this reprocessing means recycling the tailings through the threshing, separating and cleaning means. However, during recent years, the size, and more especially the capacity of combines have increased. This means that the threshing, separating, and cleaning means have to be capable of handling considerably increased volumes of crop material. With the present large capacity machines, even small percentages of tailings still represent a considerable volume. Recycling these volumes of tailings through the threshing, separating and cleaning means often leads to an uneven loading and/or an overloading of the various components both of which are disadvantageous as both ultimately result in considerable losses.
For recycling the tailings through the threshing means, commonly a paddle-type tailings elevator is provided between the cleaning mechanism and the threshing means. This elevator is normally relatively large and hence relatively expensive.
In other known combine harvesters, independent tailings rethreshers have been provided which are normally arranged to receive the tailings from the cleaning mechanism and to discharge the rethreshed tailings to a grain pan of the cleaning mechanism for recycling the tailings through this cleaning mechanism. The provision of separate tailings re-threshing means of this type is advantageous in as far as the main threshing mechanism can be used to its full capacity without any risks for unevenly loading or overloading it with tailings. These separate tailings rethreshers have proved advantageous especially in combination with high capacity combines since they enable components to operate with a maximum efficiency. Nevertheless, these separate tailings rethreshers have some disadvantages the main one of which is that certain embodiments are complicated and hence expensive. One such embodiment combines a conventional type elevator with rethresher means. Another embodiment combines rethresher means with a vertical auger for feeding the tailings to the rethresher on top thereof. The latter structure is driven via a drive transmission including conical gears which adds to the expense.
All known tailings rethreshers comprise a rotor cooperable with stationary elements to rethresh the tailings, on the one hand, and operable to discharge the rethreshed tailings and spread them substantially evenly over a grain pan of the grain cleaning means for recycling through the latter, on the other hand. Therefore, the design of the rotor has been a compromise so as to fulfil both functions to an acceptable degree.
In operation, the rotor moves the tailings over an aggressive surface thereby effecting rethreshing. The aggressive surface in some of the known tailings rethreshers extends only over a small arc so as to accommodate an inlet and an outlet opening. Thus the efficiency of such a rethresher is relatively low. In other arrangements, the aggressive surface is larger but the rotor is incapable of moving the tailings over the entire surface, whereby the maximum efficiency is not realized.
Another disadvantage is that the tailings are supplied to the tailings rethresher rotor, either co-axially or in a direction generally parallel to the rotor axis. Thus the tailings are not evenly spread over the entire width of the rethreshing rotor and the associated aggressive surface which again reduces efficiency.